package com.dylan.历史.多线程.并发编程的艺术.锁;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/**
 * Created by Dylan on 2018/9/19.
 *
 * 实现独占锁
 */
public class Mutex implements Lock {

    /**
     * 定义同步器并重写相应方法，使用内部类的方式组合到同步组件中
     */
    private class Sync extends AbstractQueuedSynchronizer {

        @Override
        protected boolean tryAcquire(int arg) {
            if (compareAndSetState(0, 1)) {
                setExclusiveOwnerThread(Thread.currentThread());
                return true;
            }
            return false;
        }

        @Override
        protected boolean tryRelease(int arg) {
            if (Thread.currentThread() != getExclusiveOwnerThread()) {
                throw new IllegalMonitorStateException();
            }
            setExclusiveOwnerThread(null);
            setState(0);
            return true;
        }

        @Override
        protected boolean isHeldExclusively() {
            // 该方法ConditionObject会使用
            return Thread.currentThread() == getExclusiveOwnerThread();
        }

        Condition newCondition() {
            return new ConditionObject();
        }

    }

    // 创建独占锁时创建同步器对象
    private final Sync sync = new Sync();

    @Override
    public void lock() {
        sync.acquire(1);
    }

    @Override
    public void lockInterruptibly() throws InterruptedException {
        sync.acquireInterruptibly(1);
    }

    @Override
    public boolean tryLock() {
        return sync.tryAcquire(1);
    }

    @Override
    public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
        return sync.tryAcquireNanos(1, unit.toNanos(time));
    }

    @Override
    public void unlock() {
        sync.release(1);
    }

    @Override
    public Condition newCondition() {
        return sync.newCondition();
    }
}
